1. Field of the Invention
The present invention relates to a card recording medium containing a magnetic card such as a credit card, a cash card, an identification (ID) card or the like, and particularly to a certifying method for certifying whether owner's card recording medium is true or not, a card recording medium enciphering system for enciphering ID (Identification) information recorded on a magnetic card, a card recording medium in which personal data (which are transformed to character data) and a photograph of the face of a user are recorded, and a recording medium in which a forming method and an enciphering method for the card recording medium are recorded as computer programs.
2. Description of Prior Art
Japanese Laid-open Patent Application No. Sho-64-76270 discloses one of techniques for verifying a true owner of a magnetic card such as a credit card, a cash card or the like, and one of enciphering systems for enciphering magnetic card ID information. According to the technique and the enciphering system as disclosed in the above publication, in order to enhance security when a holder of a magnetic card such as a credit card, a cash card or the like is confirmed, value information such as an amount of money to be drawn out, ID information which is desired to be recorded as magnetic information on the magnetic card, etc. are enciphered and recorded in the magnetic card in advance. In order to actually confirm whether the holder of the magnetic card is a true owner or not, the ID information recorded in the magnetic card is decoded from the magnetic card, and compared with ID information which is separately and directly input by the holder to verify whether the holder of the magnetic card is the true owner or not. (This publication is hereinafter referred to as "first prior art").
FIG. 20 is a block diagram showing a conventional magnetic card ID information enciphering system.
The operation of the conventional magnetic card ID information enciphering system will be described with reference to FIG. 20.
Enciphering means 72 enciphers ID information 71 (encipherment may be performed in any one of various ways) so that the ID information data cannot be easily analyzed by merely reading out the magnetic information of the ID information 71 from the magnetic card. Magnetic information forming means 73 records the magnetic information (enciphered ID information) generated by the enciphering means 72 at a magnetic recording portion (magnetic stripe or the like) on the magnetic card.
Further, Japanese Laid-open Patent Application No. Hei-06-135187 discloses a magnetic card on which a face photograph of an owner is printed on the card in addition to the magnetic data which are originally recorded in the magnetic card, and also data of enciphered photographic information are printed. In the technique as disclosed in this publication, the card contains an image region where the outlook information of the owner is displayed, and a scramble region where enciphered information obtained by transforming the image information on the basis of a predetermined logic is displayed. The enciphered photographic information is decoded by using an inverse logic to verify the identification between the decoded photographic information and the image information of the photograph of the face, thereby mechanically verifying the justice of the card. (This publication is hereinafter referred to as "second prior art").
Further, identification cards with photographs such as passports, identification cards of employees of companies, various kinds of licenses, etc. have recently propagated. Further, a credit card to which a photograph is attached has also propagated. These cards are generally called as "ID cards". Particularly, an ID card with a photograph which is issued by an official organization is used for identification. However, such an ID card may be forged. In fact, with respect to even present compact passports which are designed to be hardly imitated, there have appeared forged passports each of which is obtained by merely replacing a photograph with another in the compact passport. In addition, the forged passports are designed very elaborately and thus it is very difficult to look through the fake.
Two reasons are considered as the reason why forged ID cards containing the forged passports are formed. (1) A photograph attached onto the ID card can be replaced by another. (2) There is no relation between the photograph and the item described on the ID card. In other words, even if only the photograph is replaced by another and the other mentioned items are not changed, it is not identifiable at a glance whether the ID card is true or forged.
In order to overcome this drawback, there are needed (a) a method of forming an identification card so that a forging action itself to the ID card is difficult, and (b) a method of preventing use of a forged identification card by checking the forgery of the identification card even when the card is forged.
Here, Japanese Laid-open Patent Application No. Hei-3-193495 disclosed an example of the method (a) (hereinafter referred to as "third prior art"). This publication discloses an ID card issuing system using an image processing device taking face photograph information, attribute information, layout information, etc. In this ID card issuing system, not only the above information, but also forgery preventing information are subjected to image processing to form an image pattern, then a complicated pattern is superposed on a photograph, and then the overlapped photograph is printed on the ID card. In this method, the pattern to be superposed on the photograph is complicated to prevent the forgery.
Further, an example of the method (b) is disclosed in a fifth embodiment of Japanese Laid-open Patent Application No. Hei3-185585 (hereinafter referred to as "fourth prior art"). In this case, identification data for judging whether an identification card is true or forged are prepared on the basis of data described on the identification card, and the identification data are superposed on the photographic portion of the identification card and printed. According to this method, the mentioned items of the identification card and the identification data superposed on the photograph can be collated with each other. Therefore, even when the photograph is replaced by another, the forgery can be found out.
Further, Japanese Laid-open patent Application No. Hei-3-185585 discloses a method of embedding the identification data into the photograph. The identification data are determined by a calculation based on the mentioned items, and the data thus determined are embedded into a part of the photograph.
From another point of view, if a photograph printed on an ID card is judged to be normal, it can be judged whether the ID card is true or forged. Therefore, there has been proposed a method of frequency-transforming an image and embedding digital watermark data into frequency spectrum ("Nikkei Electronics" Apr. 22, 1996 (No. 660) p13, "Nikkei Electronics" Feb. 24, 1997 (No. 683) pp99-124) (hereinafter referred to as "fifth prior art").
In this method, an original work is frequency-transformed by DCT or Fast Fourier Transform, and the frequency spectrum is added with ID information of a random number inherent to each user to thereby spectrum spreading. Since the frequency spectrum containing the ID information is subjected to inverse frequency transformation and then the frequency spectrum having the ID information hidden therein and the frequency spectrum of the original work are differentiated, whereby the ID information is generated. Therefore, comparing the ID information with the normal ID information, it can be judged whether this ID conformation is an original work which is legally gained.
The electronic watermark is embedded into the frequency component while this ID information is set as the frequency spectrum of the low frequency component, and thus the electrical water mark is not lost even by the image processing such as the compression processing, the filtering processing, etc. Further, the random numbers which are conformed with the normal distribution are used as the electronic watermark to prevent the interference between the electronic watermark data, thereby making it difficult to break down the electronic watermark without having a great effect on image quality.
The embedding method of the electronic watermark data is as follows. First, an original image is transformed to frequency components by using discrete cosine transformation (DCT) or the like, and data of n which indicate high values in the frequency area are selected as f(1), f(2), . . . , f(n).
Subsequently, the electronic watermark data w(1), w(2), . . . , w(n) are selected from the normal distribution of 0 in average value and 1 in dispersion value, and the following equation is calculated for each frequency component: EQU F(i)=f(i)+.alpha..vertline.f(i).vertline.*w(i)
Here, .alpha. represents a scaling element. Finally, the frequency component in which f(i) is replaced by F(i) is subjected to inverse discrete cosine transformation to obtain an image into which the electronic watermark data are embedded.
The detection of the electronic watermark data is performed by the following method. In this detection method, the original image and electronic watermark data candidates w(i) (i=1, 2, . . . , n) must be known.
First, an image with electronic watermark data is transformed to frequency components by using DCT or the like. Subsequently, the electronic watermark data w(i) is calculated and extracted from f(i) and F(i) by the following equation: EQU W(i)=(F(i)-f(i))/f(i).
Subsequently, the statistical similarity of w(i) and W(i) is calculated by using the inner product of vectors: EQU C=W*w/(WD*wD)
Here, W (W(1), W(2), . . . , W(n)), and w=(w(1), w(2), . . . , w(n)), (WD=the absolute value of vector W, and wD=the absolute value of vector w).
When the statistical similarity C is above a specific value, the electronic watermark data concerned are judged to be embedded.
The electronic watermark is generated from the mentioned items of the ID card, and embedded into a photograph to be printed. The electronic watermark is picked up from the photograph at the detection time, and compared with the mentioned items to judge whether the ID card is true or forged.
In the first prior art, the same magnetic card (a magnetic card which is regarded as being identical) can be prepared by merely reading magnetic information on a magnetic card and writing the magnetic information in a magnetic recording portion on another magnetic card like the magnetic recording portion on the magnetic card concerned. Therefore, if a third party directly copies the magnetic information, the same card can be easily prepared. Further, in the conventional magnetic card ID information enciphering system shown in FIG. 20, the ID information on the magnetic card is merely recorded as magnetic information, and thus a third party can easily copy the magnetic card concerned.
Further, in the second prior art in which a photograph is attached on a card, if it is directly copied, the same card can be prepared. Further, since data which is correlated with a face photograph is printed, the content of the card can be easily analyzed on the basis of the photograph data of the card. In the second prior art, if a photograph portion or a enciphered photograph information portion of the card is greatly scratched, the true card may be judged as a forged card. That is, in the such a conventional system that data obtained by enciphering photograph information are printed on a magnetic card, if the print data are directly copied, the same magnetic card can be prepared. Since data correlated with a face photograph are printed as "photograph information enciphered data", the content of the ID information (data obtained by enciphering photograph information) can be easily analyzed on the basis of the face photograph on the magnetic card.
Further, in the third prior art, since information for preventing forgery can be seen by a person who wants to forge the card, the person imitates a complicated pattern superposed thereon to forge the card to the level that an ordinary person cannot identify whether it is forged or not. It is possible to forge a forgery-preventing pattern in consideration of the present levels of the photograph technique, the image processing technique and the print technique. As a result, the forged ID cards cannot be identified unless there exists any clear difference in the mentioned items of the ID cards, for example, there is some difference in digit from the normal employee number, or the employee number is mentioned with Kanji although it must be originally mentioned with numerals.
In the fourth prior art, identification data which are generated from mentioned items of an ID card are printed while superposed on a photograph. According to this method, it can be judged whether the card is true or forged. However, in this case, the mentioned items and the identification data are visible data, and thus if a sufficient amount of data are collected, the calculation equation for generating the identification data from the mentioned items can be guided on the basis of both the data by the inverse operation. If this calculation equation is found out, any ID card using the same calculation equation as the ID card concerned can be forged unlimitedly. The method of embedding the identification data into the photograph is described. However, in this embodiment, the position at which the identification data are embedded is fixed, so that a forging person can easily specify the position.
In the fifth prior art using the electronic watermark, an original photograph is required, and there is no possibility that the original photograph is held together with an ID card. Accordingly, by only this technique, it is difficult to judge whether the holder of the ID card is a legal holder.